This invention relates to a process of dispersing oil soluble photograhic additives having a silver halide base, for information recording materials.
Processes of dispersing photographic additives as an alternative for introduction into silver halide materials have been found to be especially suitable for dye couplers.
In relation to the technology to be used for producing the dispersant particles herein, many processes that vary vastly among themselves may be used, such as, for example, the rotor-stator principle or the propulsion system at increased pressure. Although the preparations of dispersants have been technologically solved to a very large extent, now, as before, further investigations are necessary to stabilize the manufactured dispersant particles through the selection of appropriate high-boiling agents, auxiliary solvents and, above all, of operable surfactants and auxiliary dispersing agents, in order to prevent agglomeration and coalescence, which lead to undesirable clouding in the photographic layers.
Certain compounds, such as acid amides (aliphatic and cyclic), phthalic acid ester and phosphoric ester derivatives have been found to be effective. Their object is especially to ensure good solubility of the dye couplers and to prevent crystallization manifestations since clouding will thereby result in view of a change in the refraction coefficient. In order to facilitate solubility of the couplers in the high-boiling agents, low-boiling auxiliary solvents are most often used, which then are removed from the dispersants, for instance under reduced pressure.
The dispersing process may occur in an aqueous solution or in solutions of protective colloids. Gelatin is preferably used as the protective colloid.
The use of auxiliary dispersing agents is of absolute necessity to facilitate the dispersing process, but, above all, to stabilize the particles produced, the diameters of which, as a rule, lie between 0.1 and 0.4 .mu.m.
High standards are set for these compounds. Thus, they should stabilize the dispersing process, stabilize the particles over several weeks, exercise no photographic activity and not intrude on the coating process on production of the photographic materials. The manifold requirements are not fulfilled by most known auxiliary dispersing agents.
An overview of the auxiliary dispersing agents is, for instance, given by Gawalek in "Tensides"(Akademie Verlag Berlin 1975).
The patent literature has proposed a variety of compounds, such as, for instance, fluorine-containing surfactants in DE-OS No. 2 619 248. DE-OS No. 2 136 492, DE-OS No. 2 129 648 and DE-OS No. 2 045 464 describe anionic surfactants. These surfactants may also be used in mixtures (DE-OS No. 2 448 597). Mixtures of ionic and nonionic surfactants have been described in JP-AS No. 53-48 734, 76-25 133, DE-OS No. 1 942 873, and U.S. Pat. No. 3,676,141, wherein the nonionic surfactant is often used to advantage in the organic phase. However, polymers with surface-active qualities have also been proposed (DE-OS No. 2 820 092).
Dispersing processes for oil-soluble photographic additives which are carried out with the utilization of these compounds have definite disadvantages. Thus, most of the known auxiliary dispersing agents exhibit only inadequate stabilization effect of the dispersants, which very quickly causes enlargement of the particles with the consequent formation of cloudy layers.